#include<stdio.h>
#include<vector>
using namespace std;
int cmmdc(int a,int b)
{
    while(b)
    {
        int r=a%b;
        a=b;
        b=r;
    }
    return a;
}


FILE *in,*out;
int N,cntprim,i,j,nr,contscad;
double euler;
bool primviz[1000001];  //cele cu false sunt prime
double totprim[1000001];
double scadere[1000001];
int main()
{
    in=fopen("fractii.in","rt");
    out=fopen("fractii.out","wt");
    fscanf(in,"%d",&N);
	euler=1;
	//prim[1]=2;
	//cntprim=1;
	for(i=2;i<=N;i++)
	{
		if(!primviz[i])
		{
			euler+=2*(i-1);
			for(j=i<<1;j<=N;j+=i)
			{
				primviz[j]=true;
				if(scadere[j])
					nr=j/scadere[j];
				else
					nr=j;
				contscad=0;
				if(!totprim[j])
					totprim[j]=j;
				while( !(nr%i) && nr>1 )
				{
					nr/=i;
					contscad++;
				}
				if(nr<i)
				{
					euler+=2*( totprim[j]*(1-(double)1/i));
					totprim[j]=0;
				}
				else
				{
					totprim[j]*=(1-(double)1/i);
					scadere[j]+=contscad*i;
				}
			}
		}
	}
   /* for(i=2;i<=N;i++)
    {
		nr=i;
		double prod=i;
		for(j=1;j<=cntprim && prim[j]<=nr;j++)
		{
			if( !(nr%prim[j]) )
			{
				nr/=prim[j];
				prod*=(1-(double)1/prim[j]);
			}
		}
		euler+=2*prod;
    }*/
	fprintf(out,"%.0lf",euler);
	
    return 0;
}